fix(util/hash): add missing cast to unsigned
fix(util/hash): add missing cast to unsigned

Kha/lean,johoelzl/lean,Kha/lean,fpvandoorn/lean,dselsam/lean,Kha/lean,fpvandoorn/lean,leanprover/lean,dselsam/lean,avigad/lean,johoelzl/lean,leanprover-community/lean,dselsam/lean,leanprover/lean,dselsam/lean,fpvandoorn/lean,johoelzl/lean,fpvandoorn/lean,leodemoura/lean,avigad/lean,fpvandoorn/lean,leanprover/lean,leanprover-community/lean,digama0/lean,Kha/lean,digama0/lean,leodemoura/lean,Kha/lean,avigad/lean,digama0/lean,digama0/lean,leanprover/lean,avigad/lean,leanprover-community/lean,leanprover/lean,johoelzl/lean,leodemoura/lean,johoelzl/lean,fpvandoorn/lean,johoelzl/lean,leanprover-community/lean,avigad/lean,leanprover-community/lean,leodemoura/lean,leanprover-community/lean,leodemoura/lean,leodemoura/lean,leanprover/lean,digama0/lean,avigad/lean,digama0/lean,Kha/lean,dselsam/lean,dselsam/lean